Nuclear reactor control system



July `18, `1967 R. J. HENNIG '3,331,745

` VNUCLEAR REACTOR CONTROL SYSTEM Original Filed March 51, 1960 2 Sheets-Sheet l W' El .329i

R. J. HENNIG NUCLEAR REACTOR CONTROL SYSTEM July 18, 1967 2 heets-Sheet 2 'originar Filed March :51, 1960 IN V EN TOR. /'aerf f/Venn BY War/Ld, luefm, mman. (9A/me, /amlu P'A. rIrI United States Patent Office 3,33l,745 Patented July 18, 1967 3,331,745 NUCLEAR REACTOR CONTROL SYSTEM Robert J. Hennig, Richland, Wash., assignor to Atomic Power Development Associates, Inc., Detroit, Mich., a corporation of New York Original application Mar. 31, 1960, Ser. No. 19,011, now Patent No. 3,231,473, dated Jan. 25, 1966. Divided and this application Apr. 23, 1965, Ser. No. 450,314

6 Claims. (Cl. 176 22) This application is a division of copending application Ser. No. 19,011, filed Mar. 31, 1960, now Patent No. 3,231,473.

This invention relates to nuclear reactors and has particular reference to an improved control system for a nuclear reactor. The present invention contemplates a novel operating control system for controlling the reactivity of a reactor and also contemplates a novel safety control -system for shutting down the reactor or for immediately stopping the nuclear reaction under emergency conditions.

According to the present invention the operating control system consists of a liquid poison material and a means to regulate the level lof the liquid poison within the reactor core to control the reactivity of the reactor.

The safety control system ot' this invention, in general, comprises a plurality of rods of poison material such as boron or the like which are located within hollow tubes extending through the reactor Icore and a means for pumping liquid sodium upwardly through the tubes to hold the safety rods above the reactor core during normal operation of the reactor. A means is provided for controlling the sodium iiow rate so that the rods may be `allowed to drop gradually into the reactor core to terminate the chain reaction or, under emergency conditions, the direction of flow of sodium may be reversed so as to drive the safety rods into the reactor core at high velocity to immediately terminate the chain reaction.

The operating and control systems `disclosed herein may 'be employed in any type of nuclear reactor, for example, a reactor of the kind shown in the copending application Ser, No. 19,008 assigned to the assignee of this invention and tiled concurrently herewith, a portion of such reactor being schematically illustrated herein.

A principal object of the invention is to provide a new and improved operating control system for a nuclear reactor.

Another object of the invention is to provide a new and improved safety control system for a nuclear reactor.

Other and further objects of the invention will be apparent from the following description and claims and may :be understood by reference to the accompanying drawings, of which there are two sheets, which by way of illustration show a preferred embodiment of the invention 4and what I now consider to be the best mode of applying the principles thereof. Other embodiments of the invention may be used without departing from the scope of the present invention as set forth in the appended claims.

In the drawings: Y

FIG. 1 is a schematic illustration of the operating control system;

FlG. 2 is a schematic illustration of the safety control system; Y

FIG. 3 is a sectional view through one of the control assemblies employed in a reactor embodying the safety and control systems of the present invention;

FIG. 4 is a sectional view taken on line 4 4 of FIG. 3;

FIG. 5 is a sectional view taken on line 5 5 of FIG. 3;

FIG. 6 is a sectional view taken on line 6 6 of FIG. 3; and

FIG. 7 is a sectional view taken on line 7 7 of FIG. 6.

The operating control system is illustrated schematically in FIG. 1 in connection with a nuclear reactor which may be of the type disclosed in the above-mentioned copending application and which includes a core section 10 and a radial blanket section 12 contained within a reactor vessel 14 having an inlet 16 at its lower end for the ow of a coolant such as liquid sodium upwardly through the reactor to an outlet 18 at the upper end of the containment vessel 14. A secondary containment vessel is indicated at 20, and suitable shielding 22 may be employed as is customary.

FIG. 3 illustrates one of a series of control assemblies which may be located within the reactor core 10. The number of Icontrol assemblies and their particular location within the core may be varied according to the design of the reactor in which the control systems are used. AS shown in FIG. 3, each control assembly comprises a generally rectangular vertically disposed shell 30 which may be secured within the core of the reactor in any suitable manner such as by securing the same to the adjacent fuel subassemblies making up the reactor core 10. The control assembly includes a pair of operating control tubes 32 closed at their upper ends and open at their lower ends to communicate with a pipe 34 leading to a header 36. A pipe 38 extends from the header 36 upwardly along the inside wall of the reactor vessel and passes out through the head 40 of the reactor vessel and through the secondary containment tank 20. A pipe 42 connected to the pipe 38 leads to the lower end of a cylinder 44 containing a piston 46 which is loosely fitted within the cylinder 44. A line 48 leads from the pipe 42 to the lower end of a collection and purge tank 50. The entire system thus far described is illed with a liquid poison material su-ch as lithium-6, and the liquid is normally maintained within the cylinder 44 and .the operating control tubes 32 at the level indicated by the line 52 in FIG. 1. The system may -be filled and drained by means of a valve 54. v

The piston 46 is provided with a piston rod 56 which is connected at its upper end to a gas cylinder actuating device S8 and to a rack -60 meshed with a pinion 62 which may be driven when required through an electric motor or other power source, not shown. The level of the liquid lithium is adjusted as required by moving the piston 46 downwardly within the cylinder 44 when the level is to be raised to decrease the reactivity of the reactor and by raising the piston 46 when the liquid level is to be lowered to increase the reactivity. The gas cylinder 58 may be connected to a suitable source of hydraulic pressure, not shown, so that the piston rod 56 may be moved upwardly or downwardly as required upon proper connection of the cylinder 58 to the source of pressure. The cylinder 58 may be employed for relatively short and rapid strokes of the piston 46 to obtain small variations of the volume of the poison material within the reactor core. The pinion 62 andthe rack 60 may be employed for obtaining longer and slower strokes of the piston 46. The rack 60 is secured to the cylinder 58 so that movement of the rack imparts movement to the piston rod 56 and the piston 46.

The control tubes 32 may be made of stainless steel provided with a coating of columbium on all interior surfaces to prevent corrosion of the tubes by the poison material. A small diameter tube 70 is disposed within each of the operating control tubes 32. The tubes 70` are open at their upper ends which terminate adjacent the closed upper ends of the tubes 32. The tubes 70 within each pair of operating control tubes 32 are joined at their lower ends into a single tube 71 which passes through the pipe 34 and connects into a similar small diameter tube located within the header 36 and passing through the pipes 38, 42 and 48 back to the collection Y and purge tank 50. The tubes 70 and 71 may be made of the lithium or other poison material and are indicated by the dotted lines in FIG. l. The tubes 70 and 71 are designed to carry off any helium that may collect in the upper ends of the control tubes 32 due to neutron absorption in the lithium and are also designed to equalize the pressure within the several tubes making up the operating control system.

The safety control system is illustrated schematically in FIG. 2 and is shown in conjunction with a reactor of the kind previously described. As shown in FIG. 3, each control assembly includes a plurality of elongated vertically disposed tubes 74 with the lower portions of the tubes 74 located within and supported by the shell 30. The tubes 74 are supported at their lower ends on a support plate 76 which extends across the upper end of a header 78 connected to a supply pipe 80. Each group of tubes 74 is provided with an outlet header 82 connected to an outlet pipe S4.

A poison rod 86 is disposed within each of the tubes 74 and may consist of a slug or rod of solid boron carbide in a perforated stainless steel jacket. The rods 86 are of smaller diameter than the inside diameter of their respective tubes 74 to pro-vide a clearance between the rods 86 and the tubes 74. A retaining plate 9d extends across the outlet header 82 to limit upward travel of the rods 36. The supply pipes S of adjacent groups of safety control tubes are connected to a common supply header 92, while the outlet pipes 84 of adjacent groups of tubes are connected to a common outlet header 94. Two groups of tubes 74 are illustrated schematically in FIG. 2, one group of tubes being indicated at 96 and the other at 98, with the two groups of tubes 96 and 98 having common inlet and outlet headers 92 and 94.

Each two groups of safety control tubes 96 and 98 are connected into a closed circuit, as illustrated in FIG. 2. The inlet header 92 is connected to an inlet pipe 100, while the outlet header is connected to a return line 162. The system includes a storage tank 104 and a pump 106 having its inlet connected to a line 108 leading from the tank 104 and its outlet connected to the supply line 100 through a shut-off valve 110 and a three-way valve 112. During normal operation of the reactor the valve 110 is open and the valve 112 is set so that liquid sodium or other suitable material contained within the tank 104 will be supplied from the pump 106, past valve 112 to line 114 which opens into a line 116 connected at its lower end to the inlet pipe 100 and at its upper end to a three-way valve 11S, the latter preventing flow through line 116 under normal operating conditions. The liquid sodium is thus pumped upwardly through the tubes 74 and is returned through the return line 102, a line 120, past valve 118 into the tank 164, and back to the pump 106 through line 108.

The sodium is circulated by the pump 166 at such a rate as to maintain the poison rods 86 at the upper ends of the tubes 74 where they engage the retaining plate 90, the rods being held against downward movement by the upward flow of sodium through the tubes 74. The rods 86 closest to the center of the reactor core may have a greater clearance within their tubes 74 than the remaining rods S6, and such clearance may be progressively decreased from the radially innermost rods 86 to those more remote from the center of the reactor core. Thus, in the event of a reactor shutdown, the velocity of the sodium ow may be decreased so that the innermost rods 86 will fall into the reactor core first and as the flow velocity is further decreased, the remaining rods 86 Will drop by gravity until the reactor is completely shut down.

In the event of an emergency condition the direction of ow through the circuit may be reversed by manipulation of valves 112 and 118. In such case the rods 86 will be immediately driven downwardly into the reactor core to terminate the chain reaction. When the positions of the valves 112 and 118 are reversed, the line 114 is closed by valve 112 and a line 122 is opened, thereby connecting the return line 162 to the pump outlet. Line is closed by valve 118 at such time, while line 116 is opened through the valve 11S, thereby obtaining an immediate reversal of ow in the lines 180 and 102 to drive the safety rods into the reactor core.

As shown in FIG. 7, each of the safety rods 86 is provided at its lower end with an upwardly opening recess forming a dashpot chamber. The lower support plates 76 are provided with tapered plugs 132 which extend upwardly therefrom in axial alignment with each of the safety rods 86. This arrangement provides a dashpot or decelerating effect to the rods 86 as they reach the lower ends of the tubes 74. The liquid sodium within the dashpot chamber 130 must be forced out past the restricted annular opening 134 between the wall of the chamber 130 and the tapered plug 132, thereby slowing down the rod and cushioning the same as it reaches its lowermost position against the support plate 76.

The safety control rods are thus hydraulically actuated and controlled rather than being actuated by mechanical devices. The operating control system likewise is a hydraulic system rather than employing solid rods which must be moved by mechanical actuating devices into and out of the reactor core. This arrangement possesses many advantages such as elimination of the necessity of mounting mechanical actuating devices in axial alignment with solid rods at the top or -bottom of the reactor. With the hydraulic systems disclosed herein, the piping may enter and leave the reactor vessel at any arbitrary point and the yactuating mechanisms may be located outside of the reactor vessel while maintaining the operating and safety controls in the most effective position thereof within the reactor core. While only a single safety control circuit has been illustrated, it is contemplated that two or more independently operable safety control circuits may be employed in the reactor to provide an added safety factor in the event of failure of one of the systems.

While I have illustrated and described a preferred embodiment of my invention, it is understood that this is capable of modification, and I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

I claim:

1. In a nuclear reactor including an active portion capable of sustaining a nuclear fission chain reaction, a control system for regulating the reactivity of said active portion of said reactor, comprising a plurality of tubes extending upwardly into said active portion, said tubes being closed at their upper ends, piping connecting the lower ends of said tubes to a supply of liquid poison material, control means for controlling the level of the liquid in said tubes to regulate the reactivity of said active portion, a pipe extending upwardly through each of said tubes, said pipes having openings therein above the level of said liquid in said tubes, and said pipes being interconnected and operable for withdrawing gases formed by the transmutation of the liquid poison material that collects in the upper portion of said tubes and for equalizing the pressures within said tubes.

2. In a nuclear reactor including an active portion capable of sustaining a nuclear ssion chain reaction, a control system for regulating the reactivity of said active portion of said reactor, comprising a plurality of tubes extending upwardly into said active portion, said tubes being closed at their upper ends, piping connecting the lower ends of said tubes to a supply of liquid poison material, said supply of liquid material being subjected to pressure, means for releasing the pressure in the upper ends of said tubes, and control means interconnected with said piping outside of said active portion for controlling the level of the liquid in said tubes to regulate the reactivity of said active portion.

3. In a nuclear reactor including an active portion capable of sustaining a controlled nuclear ssion chain reaction, a control system for regulating the reactivity of said active portion of said reactor, comprising a tube extending upwardly into said active portion and containing a liquid poison material, control means for controlling the level of the liquid in said tube to regulate the reactivity of said active portion, said control system including a cylinder disposed remotely of said active portion and containing a supply of liquid poison material, a pipe interconnecting said tube to said cylinder, a piston mounted in said cylinder and reciprocably movable to control the liquid level in said cylinder and thereby control the liquid level in said tube for controlling the nuclear fission chain reaction.

4. In a nuclear reactor including an active portion capable of sustaining a nuclear fission chain reaction, a control system for regulating the reactivity of said active portion of said reactor, comprising a plurality of tubes extending upwardly into said active portion, said tubes being closed at their upper ends, a first pipe connecting the lower ends of said tubes to a supply means of liquid poison material, said supply means of liquid poison material includes a cylinder containing said liquid poison material, a piston mounted in said cylinder, means for moving said piston in one direction in said cylinder to force said liquid poison material from the cylinder through said rst pipe into said tube and in an opposite direction in said cylinder to provide space for receiving the liquid poison material from said tube via the first pipe and thereby regulate the liquid level in said tube, a collection and purge tank, and a second pipe extending upwardly through each of said tubes, said second pipes having openings therein above the level of said liquid in said tubes, and said second pipes being interconnected and disposed inside said first pipe, the interconnected portion of the second pipe terminating in said collection and pur-ge tank.

5. In a nuclear reactor including an active portion capable of sustaining a nuclear fission chain reaction, a control system for regulating the reactivity of said active portion of said reactor, comprising a plurality of tubes extending upwardly into said active portion, said tubes being closed at their upper ends, a cylinder containing a supply of liquid poison material, a pipe interconnecting the lower ends of said tubes to said cylinder so that the level of the liquid in said cylinder controls the level of the liquid in said tubes, and a piston movable in one direction in said cylinder to force said liquid poison material from the cylinder through said first pipe into said tube and in an opposite direction in said cylinder to provide space for receiving the liquid poison material from said tube via the first pipe to regulate the liquid level in the tubes, a pipe extending upwardly through each of said tubes, each of said pipes having openings therein above the level of said liquid in said tubes, said pipes being connected at their other ends and operable for withdrawing gases from the upper ends of said tubes and for equalizing the pressures Within said tubes.

6. A nuclear reactor according to claim 2 wherein said liquid poison material is liquid lithium.

References Cited UNITED STATES PATENTS 2,979,450 4/ 1961 Dusbabek 176-52 2,982,712 5/1961 Heckman 176-52 2,990,358 6/ 1961 Manley 176--86 3,025,228 3/1962 Whitelaw 17686 3,183,168 5/1965 Bell 176-42 FOREIGN PATENTS 1,269,659 7/1961 France. 1,125,562 3/ 1962 Germany.

799,001 7/1958 Great Britain.

921,447 3/ 1963 Great Britain.

923,921 4/1963 Great Britain.

OTHER REFERENCES Schultz: Control of Nuclear Reactors and Power Plants, second edition, 1961, pp. 241, 242.

CARL D. QUARFORTH, Primary Examiner.

LEON D. ROSDOL, L. DEWAYNE RUTLEDGE,

Examiners.

H, E, BEHREND, Assistant Examiner. 

1. IN A NUCLEAR REACTOR INCLUDING AN ACTIVE PORTION CAPABLE OF SUSTAINING A NUCLEAR FISSION CHAIN REACTION, A CONTROL SYSTEM FOR REGULATING THE REACTIVITY OF SAID ACTIVE PORTION OF SAID REACTOR, COMPRISING A PLURALITY OF TUBES EXTENDING UPWARDLY INTO SAID ACTIVE PORTION, SAID TUBES BEING CLOSED AT THEIR ENDS, PIPING CONNECTING THE LOWER ENDS OF SAID TUBES TO A SUPPLY OF LIQUID POISON MATERIAL, CONTROL MEANS FOR CONTROLLING THE LEVEL OF THE LIQUID IN SAID TUBES TO REGULATE THE REACTIVITY OF SAID ACTIVE PORTION, A PIPE EXTENDING UPWARDLY THROUGH EACH OF SAID TUBES, SAID PIPES HAVING OPENINGS THEREIN ABOVE THE LEVEL OF SAID LIQUID IN SAID TUBES, AND SAID PIPES BEING INTERCONNECTED AND OPERABLE FOR WITHDRAWING GASES FORMED BY THE TRANSMUTATION OF THE LIQUID POISON MATERIAL THAT COLLECTS IN THE UPPER PORTION OF SAID TUBES AND FOR EQUALIZING THE PRESSURES WITHIN SAID TUBES. 